1. Field of the Invention
The present invention relates to a discharge determination device and method, and more specifically to a discharge determination device and method suitable for determining discharge errors in a discharge head having a plurality of droplet discharge ports (nozzles).
2. Description of the Related Art
An inkjet type recording apparatus forms images on a recording medium by discharging ink from nozzles while moving a print head having a plurality of nozzles and a recording medium relatively with respect to each other. In an apparatus of this kind, discharge errors may arise, namely, ink may cease to be discharged from the nozzles, or the amount of ink discharged (the dot size deposited on the recording medium) or the position at which the ink is deposited may become defective, as a result of increase in the viscosity of the ink, infiltration of air bubbles into the ink, or the like. Therefore, technology for determining whether or not ink droplets have been discharged from nozzles and for restoring discharge failures have been proposed (see Japanese Patent Application Publication Nos. 5-131644 and 11-286124).
The inkjet heads disclosed in Japanese Patent Application Publication Nos. 5-131644 and 11-286124 have piezoelectric elements for applying pressure required in order to discharge ink, and ink discharge failures are determined from the response of the piezoelectric elements after an ink discharge operation (after pressurization).
Furthermore, Japanese Patent Application Publication No. 11-129472 proposes an inkjet recording apparatus provided with an ink end detector which detects the end of ink accurately, in such a manner that the ink inside a cartridge can be used without creating waste. More specifically, the inkjet head disclosed in Japanese Patent Application Publication No. 11-129472 comprises a plurality of nozzles, discharge chambers connected to the respective nozzles, and a reservoir (common liquid chamber) connected to the discharge chambers. Ink droplets are discharged from the nozzles by generating a pressure inside the discharge chambers. A diaphragm which can deform in accordance with the pressure inside the discharge chambers is formed in one part of the reservoir. A semiconductor diffusion resistance type pressure sensor is provided in the diaphragm, and change in the resistance value measured by the sensor is determined by a determination circuit. If a change in the resistance value equal to or exceeding a prescribed amount is detected, then an ink end reporting device informs the user that the ink has ended.
The principal reason for ink discharge ceasing to function normally is the presence of air bubbles inside or in the vicinity of the pressure chambers (which correspond to the “discharge chambers” in Japanese Patent Application Publication No. 11-129472). Since the air bubbles absorb the pressure by changing volume, then the pressure generated by the actuators for ink discharge cannot be used efficiently in order to discharge the ink. Consequently, it is possible to ascertain the discharge status by determining whether or not air bubbles are present inside or in the vicinity of the pressure chambers, and whether or not the pressure generated by the actuators is being transmitted to the ink as intended.
On this point, in Japanese Patent Application Publication Nos. 5-131644 and 11-286124, the piezoelectric effect of the piezoelectric elements (piezo elements) used to create discharge pressure is taken as a basis for determining whether or not discharge has occurred. It is judged whether or not discharged has been carried out normally by observing the determination signal after discharge driving (after pressurization). However, these publications do not disclose the acquisition of a determination signal during pressurization. Supposing that it were attempted to determine the status during pressurization by means of the composition described in Japanese Patent Application Publication No. 5-131644 or 11-286124, the circuit composition would become extremely complicated.
On the other hand, Japanese Patent Application Publication No. 11-129472 determines the change in the negative pressure when the ink separates, accurately, by providing a sensor in the reservoir near the discharge chambers. However, it does not determine ink discharge errors.